Supplemental Financial Information - Statement of Operations (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Operating revenues [Abstract]
Total operating revenues	$ 6,082		$ 4,690
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	277		194
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	(9)		(22)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	36	[1]	60	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	14	[1]	48	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	195		247
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	64		65
Net unrealized income (losses) on pledged assets	2		35
Regulatory offset to decommissioning trust fund-related activities	(190)	[2]	(277)	[2]
Total decommissioning-related activities	121		178
Investment income	3		4
Long-term lease income	8		7
Interest income related to uncertain income tax positions	25		0
AFUDC - equity	6		3
Bargain purchase gain related to Wolf Hollow acquisition			0
Other	9		2
Other, net	172		194
Exelon Generation Co L L C [Member]
Operating revenues [Abstract]
Total operating revenues	3,533		2,743
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	93		73
Equity Method Investment Summarized Financial Information Gross Profit Loss [Abstract]
Total income (loss) in equity method investments	(9)		(22)
Decommissioning-Related Activities [Abstract]
Net realized income on decommissioning trust funds - Regulatory Agreement Units	36	[1]	60	[1]
Net realized income on decommissioning trust funds - Non-Regulatory Agreement Units	14	[1]	48	[1]
Net unrealized income (losses) on decommissioning trust funds - Regulatory Agreement Units	195		247
Net unrealized income (losses) on decommissioning trust funds - Non-Regulatory Agreement	64		65
Net unrealized income (losses) on pledged assets	2		35
Regulatory offset to decommissioning trust fund-related activities	(190)	[2]	(277)	[2]
Total decommissioning-related activities	121		178
Investment income	(2)		0
Interest income related to uncertain income tax positions	5		0
Bargain purchase gain related to Wolf Hollow acquisition			0
Other	4		0
Other, net	128		178
Commonwealth Edison Co [Member]
Operating revenues [Abstract]
Total operating revenues	1,160		1,388
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	74		75
Decommissioning-Related Activities [Abstract]
Investment income	0		1
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	3		1
Other	2		2
Other, net	5		4
PECO Energy Co [Member]
Operating revenues [Abstract]
Total operating revenues	895		875
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	41		31
Decommissioning-Related Activities [Abstract]
Investment income	0		1
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	1		1
Other	2		0
Other, net	3		2
Baltimore Gas and Electric Company [Member]
Operating revenues [Abstract]
Total operating revenues	880		697
Taxes Excluding Income And Excise Taxes [Abstract]
Total taxes other than income	55		48
Decommissioning-Related Activities [Abstract]
Investment income	2	[3]	3	[3]
Interest income related to uncertain income tax positions	0		0
AFUDC - equity	2		3
Other	1		0
Other, net	$ 5		$ 6

[1] Includes investment income and realized gains and losses on sales of investments of the trust funds.

[2] Includes the elimination of NDT fund-related activity for the Regulatory Agreement Units, including the elimination of net income taxes related to all NDT fund activity for those units. See Note 13 of the Exelon 2012 Form 10-K for additional information regarding the accounting for nuclear decommissioning.

[3] Relates to the cash return on BGE’s rate stabilization deferral. See Note 5 - Regulatory Matters for additional information regarding the rate stabilization deferral.